nucleic acids Flashcards
name the type of bond between:
i) complementary base pairs
ii) adjacent nucleotides in a DNA strand
i) hydrogen bonds;
ii) phosphodiester bonds;
describe the structure of DNA. (5)
- polymer of nucleotides;
- each nucleotide formed from deoxyribose, a phosphate group and an organic/nitrogenous base;
- phosphodiester bonds between nucleotides;
- double helix/2 strands held by hydrogen bonds;
- hydrogen bonds/pairing between adenine, thymine and cytosine, guanine;
describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (2)
- condensation reaction/loss of water;
- between phosphate and deoxyribose;
- catalysed by DNA polymerase;
name the protein associated with DNA in a chromosome. (1)
histones;
in the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. each then acts as a template for the formation of a new complementary strand.
describe how the separation of stands occurs. (2)
- DNA helicase;
- breaks hydrogen bonds between base pairs/ AT and GC/complementary bases;
OR
breaks hydrogen bonds between polynucleotide strands;
describe the role of DNA polymerase in the semi-conservative replication of DNA. (2)
- joins (adjacent DNA) nucleotides;
- (catalyses) condensation reactions;
- (catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
name the two scientists who proposed models of the chemical structure of DNA and of DNA replication. (2)
watson and crick;
a scientist replicated DNA in a test tube. to do this, he mixed an enzyme with identical single-stranded DNA fragments and a solution containing DNA nucleotides.
name the enzyme used in this DNA replication. (1)
DNA polymerase;
use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of the DNA nucleotides
role of single-stranded DNA fragments
1. template;
2. determines order of nucleotides/bases;
role of DNA nucleotides
3. forms complementary pairs / A-T, G-C;
OR
forms complementary DNA strand;
give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. (2)
- weak/easily broken by hydrogen bonds between bases allow two strands to separate/unzip;
- two strands, so both can act as templates;
- complementary base pairing allows accurate replication;
describe the role of two named enzymes in the process of semi-conservative replication of DNA. (3)
- DNA helicase causes breaking of hydrogen bonds between DNA strands;
- DNA polymerase joins the DNA nucleotides;
- forming phosphodiester bonds;
the enzymes DNA helicase and DNA polymerase are involved in DNA replication.
describe the functions of each of these enzymes.
DNA helicase
DNA polymerase
- DNA helicase - (unwinding DNA and)breaking hydrogen bonds between chains/bases/strands;
- DNA polymerase - joins (adjacent) nucleotides OR forms phosphodiester bond/sugar-phosphate backbone;
adenosine triphosphate (ATP) is a nucleotide derivative.
contrast the structure of ATP and a nucleotide found in DNA to give two differences.
- ATP has ribose and DNA nucleotide has deoxyribose;
- ATP has 3 phosphate groups and DNA nucleotide has 1 phosphate group;
- ATP - base always adenine and in DNA nucleotide base can be different/varies;
use your knowledge of enzyme action to explain why the arrows point in opposite direction during DNA replication. (4)
- DNA has antiparallel strands;
- shape of nucleotides is different/nucleotides aligned differently;
- enzyme has active sites with specific shape;
- only substrates with complementary shape/only the 3’ end can bind with active site of enzyme/ active site of DNA polymerase;
use your knowledge of enzyme action and DNA replication to explain why new nucleotides can only be added in a 5’ to 3’ direction. (4)
- reference to DNA polymerase;
- (which is) specific;
- only complementary with/binds to 5’ end (of strand);
- shape of 5’ end and 3’ are different/description of how different;
